CN106253618B

CN106253618B - Surface groove patterns for permanent magnet motor rotors

Info

Publication number: CN106253618B
Application number: CN201610397788.3A
Authority: CN
Inventors: 梁峰; 郭鲁肃; 迈克尔·W·德格内尔
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2015-06-09
Filing date: 2016-06-07
Publication date: 2020-04-17
Anticipated expiration: 2036-06-07
Also published as: DE102016109584A1; US9985484B2; US20160365762A1; CN106253618A

Abstract

The present disclosure relates to a surface groove pattern for a permanent magnet motor rotor. A permanent magnet electric machine includes a rotor configured to rotate about an axis. The rotor is composed of a plurality of axially stacked layer sections. Each layer section is composed of axially stacked laminations defining a pattern of axial grooves on the outer surface of the rotor to reduce torque ripple. The pattern is different for at least two layer portions. The pattern of each layer portion may be alternately arranged with respect to the magnetic poles of the rotor.

Description

Surface groove patterns for permanent magnet motor rotors

Technical Field

The present application relates generally to surface groove patterns for permanent magnet electric machine rotors.

Background

Hybrid electric vehicles and electric vehicles use one or more electric machines to provide propulsion for the vehicle. A variety of motor technologies are available for this application. Permanent magnet motors are a typical choice for vehicular applications. The permanent magnet motor includes a stator and a rotor. The rotor is configured with permanent magnets. The coils in the stator are energized to produce an electromagnetic flux that interacts with the electromagnetic flux produced by the permanent magnets of the rotor. The interaction of the magnetic fluxes causes the rotor to rotate. Due to various motor design characteristics, the interacting electromagnetic flux generates torque that includes harmonic components. The torque may be described as the sum of components having different frequencies. This is observed as a fluctuation or oscillation in torque. Torque ripple or torque oscillation causes vibration and noise.

Disclosure of Invention

A permanent magnet electric machine includes a rotor configured to rotate about an axis and including a plurality of layers arranged along the axis, each layer including a plurality of axially stacked laminations defining a pattern of axial grooves on a circumferential surface of each layer such that the pattern is different for at least two layers.

For at least one layer portion, the pattern may repeat over the circumferential surface with an arc length corresponding to one pole of the rotor. For at least one layer portion, the pattern may repeat over the circumferential surface with an arc length corresponding to two poles of the rotor. For at least one layer portion, the pattern may repeat over the circumferential surface with an arc length corresponding to three poles of the rotor. The layer portions may be offset at a predetermined angle relative to adjacent layer portions such that the magnetic pole position defined by each layer portion is offset relative to the corresponding magnetic pole position of the adjacent layer portion. The set of axial grooves may be aligned in such a way that the set of axial grooves extends across the axial length of the rotor. The set of axial grooves may form at least one axial through slot extending across an axial length of the rotor within each arc length corresponding to a pole of the rotor. The pattern may alternate between adjacent layer portions. The rotor may also include a smooth layer portion without axial grooves.

A permanent magnet electric machine comprising a rotor comprising a plurality of layers arranged along an axis of rotation, each layer comprising a plurality of axially stacked laminations defining a pattern of axial grooves on an outer surface of each layer such that the pattern is different for at least two layers for an arc length of the outer surface corresponding to a pole of the rotor.

The magnetic pole may be one of a plurality of magnetic poles of the rotor, and the pattern may be repeated for each magnetic pole for at least one layer portion. The magnetic pole may be one of a plurality of magnetic poles of the rotor, and for at least one layer portion, the pattern may be alternated between adjacent magnetic poles. The set of axial grooves may be aligned in such a way that the set of axial grooves extends across the axial length of the rotor. The magnetic pole may be one of a plurality of magnetic poles of the rotor, and the magnetic pole of each layer portion may be offset at a predetermined angle with respect to the magnetic pole of an adjacent layer portion.

A permanent magnet electric machine includes a rotor including a plurality of poles arranged about an axis, each pole corresponding to a predetermined arc length of a circumferential surface of the rotor formed by a plurality of axially stacked laminations defining a pattern of axial grooves on the circumferential surface of the rotor such that the pattern is different for at least two poles.

The pattern of axial grooves of each pole may comprise at least one axial groove. The pattern may be different for each pole. The rotor may also include one pole without an axial groove. The pattern of axial grooves for each pole may comprise two axial grooves. The pattern of axial grooves for each pole may be defined by the angle between the axial grooves of each pole, and the angle may be different for each pole.

Drawings

FIG. 1 is a schematic diagram illustrating a hybrid vehicle including a typical drive train of electric machines and energy storage components.

Fig. 2A is an exemplary top view of a rotor lamination.

Fig. 2B is a side view of an exemplary rotor constructed from a series of rotor laminations and a stator constructed from a series of stator laminations.

Fig. 3 is an exemplary partial rotor lamination and partial stator lamination.

FIG. 4A is an exemplary two layer rotor design.

Fig. 4B and 4C are side views of a rotor lamination for each layer of fig. 4A.

FIG. 5 is an exemplary two layer rotor wherein one layer is smooth.

FIG. 6 is another exemplary two layer rotor, wherein the layers have different groove patterns.

FIG. 7 is an exemplary four layer rotor in which the groove pattern alternates between the layers.

FIG. 8 is an exemplary five-layer rotor in which some of the layers have different axial lengths.

FIG. 9A is an exemplary two-layer rotor prior to layer deflection.

FIG. 9B is an exemplary two-layer rotor in which the layers are deflected relative to each other.

Fig. 10 is a side view of a lamination in which the pattern of grooves is different for adjacent poles of the rotor.

Fig. 11 is an exemplary single-layer rotor in which the pattern of grooves is different for three consecutive poles of the rotor.

FIG. 12 is an exemplary two layer rotor in which the pattern of grooves for each layer alternates between the poles of the rotor.

Fig. 13 is an exemplary three layer rotor in which each layer defines a groove pattern for each three poles of the rotor.

Fig. 14 is an exemplary single-layer rotor in which the pattern of grooves is different for each pole.

Fig. 15 is an exemplary single-layer rotor in which each pole includes two axial grooves positioned at different angles.

Detailed Description

Embodiments of the present disclosure are described herein. However, it is to be understood that the disclosed embodiments are merely exemplary and that other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As one of ordinary skill in the art will appreciate, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combination of features shown provides a representative embodiment for a typical application. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations.

FIG. 1 depicts a typical plug-in hybrid electric vehicle (PHEV). The PHEV 12 may include one or more electric machines 14 mechanically coupled to a hybrid transmission 16. The electric machine 14 can operate as a motor or a generator. Further, the hybrid transmission 16 is mechanically coupled to the engine 18. The hybrid transmission 16 is also mechanically coupled to a drive shaft 20, the drive shaft 20 being mechanically coupled to wheels 22. The electric machine 14 may provide propulsion and retarding capabilities when the engine 18 is turned on or off. The electric machine 14 also functions as a generator and can provide fuel economy benefits by recovering energy that is typically lost as heat in friction braking systems. The electric machine 14 may also reduce vehicle emissions by allowing the engine 18 to operate at a more efficient speed and, in some cases, allowing the hybrid electric vehicle 12 to operate in an electric mode with the engine 18 off.

The traction battery or battery pack 24 stores energy that can be used by the electric machine 14. Typically, the vehicle battery pack 24 provides a high voltage Direct Current (DC) output. One or more contactors 42 may isolate the traction battery 24 from the high voltage bus when open and couple the traction battery 24 to the high voltage bus when closed. The traction battery 24 is electrically coupled to one or more power electronic modules 26 via a high voltage bus. The power electronics module 26 is also electrically coupled to the electric machine 14 and provides the ability to transfer energy bi-directionally between the high voltage bus and the electric machine 14. For example, the traction battery 24 may provide a DC voltage, while the electric machine 14 may operate with three-phase Alternating Current (AC) to function. The power electronics module 26 may convert the DC voltage to three-phase AC current to operate the motor 14. In the regeneration mode, the power electronics module 26 may convert the three-phase AC current from the electric machine 14 acting as a generator to a DC voltage compatible with the traction battery 24. The description herein applies equally to electric only vehicles. For an electric-only vehicle, the hybrid transmission 16 may be a gearbox connected to the electric machine 14, and the engine 18 may not be present.

The traction battery 24 may provide energy for other vehicle electrical systems in addition to providing energy for propulsion. The vehicle 12 may include a DC/DC converter module 28 electrically coupled to the high voltage bus. The DC/DC converter module 28 may be electrically coupled to the low voltage bus 56. The DC/DC converter module 28 may convert the high voltage DC output of the traction battery 24 to a low voltage DC supply compatible with the low voltage vehicle load 52. The low voltage bus 56 may be electrically coupled to the auxiliary battery 30 (e.g., a 12V battery). The low voltage system 52 may be electrically coupled to a low voltage bus 56.

The vehicle 12 may be an electric vehicle or a plug-in hybrid vehicle that may recharge the traction battery 24 via the external power source 36. The external power source 36 may be connected to an electrical outlet. The external power source 36 may be electrically coupled to a charger or Electric Vehicle Supply (EVSE) 38. The external power source 36 may be a power distribution or grid provided by a power company. The EVSE38 may provide circuitry and controls for regulating and managing the transfer of energy between the power source 36 and the vehicle 12. The external power source 36 may provide DC or AC power to the EVSE 38. The EVSE38 may have a charging connector 40 for plugging into the charging port 34 of the vehicle 12. The charging port 34 may be any type of port configured to transfer electrical power from the EVSE38 to the vehicle 12. The charging port 34 may be electrically coupled to the charger or the onboard power conversion module 32. The power conversion module 32 may regulate the power supplied from the EVSE38 to provide the appropriate voltage and current levels to the traction battery 24. The power conversion module 32 may cooperate with the EVSE38 to regulate power transfer to the vehicle 12. The EVSE connector 40 may have prongs that mate with corresponding recesses of the charging port 34. Alternatively, various components described as electrically joined or connected may transfer power using wireless inductive coupling.

One or more wheel brakes 44 may be provided to slow the vehicle 12 and prevent movement of the vehicle 12. The wheel brakes 44 may be hydraulically actuated, electrically actuated, or a combination thereof. The wheel brakes 44 may be part of a braking system 50. The braking system 50 may include other components for operating the wheel brakes 44. For simplicity, the figures depict a single connection between the braking system 50 and one of the wheel brakes 44. Implying a connection between the brake system 50 and the other wheel brakes 44. The braking system 50 may include a controller for monitoring and regulating the braking system 50. The braking system 50 may monitor the braking components and control the wheel brakes 44 for deceleration of the vehicle. The braking system 50 may be responsive to driver commands via a brake pedal, and may also operate autonomously to implement features such as stability control. When another controller or sub-function requests braking force, the controller of the braking system 50 may implement a method of applying the requested braking force.

One or more electrical loads 46 may be coupled to the high voltage bus. The electrical load 46 may have an associated controller that may operate and control the electrical load 46 when appropriate. The high voltage electrical load 46 may include a compressor and an electric heater.

The electronic modules in the vehicle 12 may communicate via one or more vehicle networks. The vehicle network may include a plurality of channels for communication. One channel in the vehicle network may be a serial bus such as a Controller Area Network (CAN). One channel in a vehicle network may include an ethernet network defined by the Institute of Electrical and Electronics Engineers (IEEE)802 series of standards. Additional channels of the vehicle network may include discrete connections between modules and may include power signals from the auxiliary battery 30. Different signals may be communicated through different channels of the vehicle network. For example, video signals may be communicated over a high speed channel (e.g., ethernet) while control signals may be communicated over CAN or discrete signals. The vehicle network may include hardware and software components that facilitate the transfer of signals and data between modules. Although the vehicle network is not shown in fig. 1, it may be implied that the vehicle network may be connected to any electronic module present in the vehicle 12. A Vehicle System Controller (VSC)48 may be present to coordinate the operation of the various components.

The electric machine 14 may be an Interior Permanent Magnet (IPM) machine that includes a stator 122 and a rotor 120. Fig. 2A depicts an exemplary rotor lamination 138, and fig. 2B depicts a side view of a stator 122 and rotor 120 configuration having a plurality of rotor laminations 138 and a plurality of stator laminations 136 arranged in an axially stacked relationship. The rotor laminations 138 may define a circular central opening 160 for receiving a drive shaft having a keyway that may receive a drive key 162. Rotor laminations 138 may define a plurality of magnet openings 142, the plurality of magnet openings 142 being symmetrically disposed with respect to adjacent pairs of magnet openings 142.

The plurality of rotor sectors 124 corresponding to the poles of the rotor may be defined by a plurality of interpole shafts (e.g., 180, 184) emanating from the central rotational axis 170 to the rotor outer circumferential surface 150 of the rotor 120. Each sector 124 may include a pair of magnet openings 142. The interpolar axes (e.g., 180, 184) may be positioned centered between adjacent magnet openings 142. It should be noted that fig. 2A only shows two of the possible

interpolar axes

180, 184, and does not show all of the possible interpolar axes. Fig. 2B depicts a series of axially stacked rotor laminations 138 stacked along a central axis 170, wherein the rotor 120 is configured to rotate about the central axis 170.

Fig. 3 depicts a partial radial cross-sectional view of a possible configuration of the rotor 120 and stator 122. In fig. 3, a partial stator lamination 136 and a partial rotor lamination 138 are depicted. The rotor laminations 138 and stator laminations 136 may be composed of a ferrous alloy. A small air gap 140 is located between the inner periphery of the stator laminations 136 and the outer circumferential surface 150 of the rotor laminations 138 (i.e., the rotor outer circumferential surface 150 of the rotor 120). The stator laminations 136 may define radially extending openings 134.

The rotor laminations 138 may define symmetrically positioned magnet openings 142 near an outer circumferential surface 150 of each rotor lamination 138. Each magnet opening 142 may be configured to receive a magnet 144. Any number of laminations may be used in a given design depending on design choice. The rotor laminations 138 and the stator laminations 136 may be arranged in a stacked manner along the axis of rotation 170. The axially stacked rotor laminations 138 and magnets 144 may define a plurality of poles distributed about an axis 170.

The stator 122 may have conductors disposed in radially extending openings 134 to form windings. The stator 122 may include a core made of stacked stator laminations 136 and a winding arrangement of conductors for carrying excitation current. The current flowing through the stator windings generates a stator electromagnetic flux. The stator flux can be controlled by adjusting the amplitude and frequency of the current flowing through the stator windings. Because the stator windings are contained in the openings 134 rather than being uniformly sinusoidally distributed along the inner circumference of the stator, there will be harmonic flux in the stator flux.

The rotor 120 may include a core made of stacked rotor laminations 138 and a set of permanent magnets 144 inserted within holes or cavities 142 defined by the core. The permanent magnets 144 in the rotor 120 may generate rotor electromagnetic flux. Due to the shape and size of the discrete permanent magnets, the rotor flux may include harmonic flux. The stator flux and the rotor flux may be distributed in the air gap 140. The interaction between the stator flux and the rotor flux causes the rotor 120 to rotate about the axis 170.

The poles of the rotor 120 may be geometrically defined to correspond to the sectors 124 defined by the rotor laminations 138. Each pole may be represented by a sector 124. The pole positions may be generally defined by a central pole axis 182 that extends radially from the axis 170 toward the outer circumferential surface 150 of the rotor lamination 138 along an intermediate location between adjacent magnet openings 142. An interpole shaft (e.g., 180, 184) may extend radially between adjacent poles from the axis 170 toward the rotor outer circumferential surface 150 of the rotor 120. The angular distance between two adjacent poles may define a pole pitch parameter. The arc length on the outer circumferential surface 150 of the rotor between two adjacent poles of the rotor may be referred to as the pole pitch. The pole pitch may be measured circumferentially about the rotor outer circumferential surface 150 between adjacent central pole shafts 182. Each pole may have an associated surface area on the rotor outer circumferential surface 150 of the rotor 120. Each pole may be represented by an arc length on the surface between adjacent

inter-pole axes

180, 184.

The electromagnetic field or signal may consist of a sum of harmonic components having different frequencies and amplitudes. Each harmonic component may be represented as a frequency and an amplitude. The signal may include a fundamental component. The fundamental component may be a frequency component having the largest amplitude.

During operation, the stator fundamental component flux and the rotor fundamental component flux may align and rotate in the same direction at the same frequency. The interaction between the fundamental components of the stator flux and the rotor flux generates torque. The stator harmonic flux and the rotor harmonic flux may have different numbers of poles, rotational speeds, and directions. As a result, the interaction between the harmonic fluxes produces torque fluctuations, referred to as torque ripple. The torque ripple may have harmonic components with different frequencies. The order of the torque ripple component may be defined as the ratio of the frequency of the torque ripple component to the rotor speed in revolutions per second.

One effect of torque ripple is that it can cause speed oscillations of the rotor. Further, torque fluctuations may affect noise and vibration of the motor and components coupled to the motor. High order torque ripple frequencies can be filtered out by the limiting bandwidth of the incorporated mechanical system. Lower harmonic frequencies of torque ripple may cause mechanical oscillations in the incorporated system. It is desirable to reduce torque ripple to reduce vibration and noise in systems including electric machines.

A typical rotor outer circumferential surface 150 of the rotor 120 is rounded or smooth. In some applications, the outer circumferential surface 150 of the rotor laminations 138 may define a pattern of axial grooves. The groove may be a channel oriented parallel to axis 170. The groove may span the axial length of the rotor outer circumferential surface 150 of the rotor 120. The effect of the notch is to reduce the amplitude of selected harmonic components of the torque while not affecting other harmonic components. In some vehicle applications, it is desirable to reduce the amplitude of certain harmonic components. The groove may be a circular shape having a predetermined depth with respect to the rotor outer circumferential surface 150. In other configurations, the grooves may have alternative shapes (such as rectangular or trapezoidal). The shape of the groove may be configured to minimize specific harmonic components.

The bonded laminations defining the same pattern of grooves on the rotor outer circumferential surface 150 may be referred to as a layer portion (section). In some rotor configurations, the rotor 120 may be constructed from a single layer portion. A subset of the one or more axial grooves may correspond to poles of the rotor 120. In some configurations, the axial grooves associated with each pole may be the same pattern. For example, the axial groove may be located at a middle position of each magnetic pole. As another example, axial grooves may be defined on both sides of the middle position of the magnetic pole at a predetermined circumferential distance. Each rotor lamination 138 may be configured to define the same groove pattern for each pole. The groove pattern defined for the magnetic poles may be repeated on the rotor outer circumferential surface as the rotor outer circumferential surface 150 is about the axis 170.

In some configurations, the rotor may be comprised of more than one layer portion. Fig. 4A depicts one pole of the two-layer rotor 212. In a two-layer rotor 212, the first layer 200 may be composed of a plurality of first rotor laminations 204 having a first circumferential groove pattern 208 as shown in fig. 4B. Second layer portion 202 may be composed of a plurality of second rotor laminations 206 having a second circumferential groove pattern 210 as shown in fig. 4C. The first layer portion 200 and the second layer portion 202 may be bonded together to form a rotor 212 having two layer portions. First circumferential groove pattern 208 may define one or more grooves at a first set of predetermined locations on the outer circumferential surface of first rotor lamination 204 relative to a mid-position (midpoint)214 of each pole. Second circumferential groove pattern 210 may define one or more grooves at a second set of predetermined locations on the outer circumferential surface of second rotor lamination 206 relative to a middle location 214 of each pole. The predetermined locations of the first set and the second set may be different such that when the first layer portion 200 and the second layer portion 202 are bonded together, the groove does not span the entire axial length of the two-layer portion rotor 212.

In some configurations, the first groove pattern 208 may be repeated for each pole. In some configurations, the first groove pattern 208 may be repeated for every two or three poles. In some configurations, the first groove pattern 208 may be different for each pole. A similar configuration is possible for the second groove pattern 210. In some configurations, a set of axial grooves may be defined across the entire axial length of the outer circumferential surface of rotor 212. The predetermined positions of the first set and the predetermined positions of the second set may comprise a set of axial grooves located at the same position relative to the intermediate position 214 of each pole.

The advantage of the multi-layer rotor configuration is that the amplitude of the multiple harmonic components can be reduced. The groove pattern of each layer portion may be configured to reduce specific harmonic frequency components. For example, the first layer portion 200 may be configured to reduce the amplitude of a first harmonic frequency component and the second layer portion 202 may be configured to reduce the amplitude of a second harmonic frequency component. By combining layer portions having different groove patterns, torque ripple resulting from multiple harmonic frequencies can be reduced.

Fig. 5 depicts one pole of an alternative two-layer rotor configuration 300. The first layer portion 302 may be comprised of a rotor lamination having a smooth outer circumferential surface. That is, the first peripheral groove pattern does not define any grooves on the surface of the first layer portion 302. The second layer portion 304 may be composed of rotor laminations defining a single groove 306 per pole. In some configurations, a single groove 306 may be located at the same position relative to the intermediate position 214 of each pole. In some configurations, the position of a single groove 306 relative to the intermediate position 214 of each pole may be different for two or more poles.

Fig. 6 depicts one pole of an alternative two-layer rotor configuration 350. The first layer portion 352 may be composed of rotor laminations defining two

slots

356, 358 per pole. The second layer portion 354 may be comprised of rotor laminations defining three

recesses

360, 362, 364 per pole. For each pole, the groove may be positioned at the same location relative to the mid-position 214 of the pole. First layer portion 352 and second layer portion 354 may be configured such that no groove spans the entire axial length of the outer circumferential surface.

In some configurations, the axial length of each layer portion of each rotor may be equal. In some configurations, the axial length of each layer portion may be different. The axial stack length may vary due to the number of laminations used for each layer. The axial length of each layer portion may affect the effect of reducing a particular harmonic component. The axial length of each layer portion may be adjusted to achieve the desired harmonic component reduction.

In some configurations, more than two layer portions may be used. Fig. 7 depicts a four-layer rotor configuration 400. In this configuration, a first rotor lamination and a second rotor lamination may be defined. The layer portions may be formed by a first rotor lamination and a second rotor lamination and arranged such that the rotor has layer portions with an alternating pattern of grooves. For example, the four-layer rotor 400 may include a first layer 402, a second layer 404, a third layer 406, and a fourth layer 408. First layer portion 402 and third layer portion 406 may be comprised of a first rotor lamination. The second layer portion 404 and the fourth layer portion 408 may be comprised of a second rotor lamination. This configuration defines a rotor circumferential surface with an alternating axial groove pattern such that adjacent layer portions have different groove patterns. In other constructions, four different rotor laminations may be defined such that each layer has a different groove pattern.

In some configurations, the rotor laminations may define a set of grooves that extend through the entire axial length of the rotor surface. In some configurations, the rotor laminations may define a set of grooves that extend through more than one continuous layer portion but do not span the entire axial length of the rotor. In some configurations, there may be no grooves extending through the entire axial length of the rotor surface.

FIG. 8 depicts a five-layer rotor configuration 450 including five layers, wherein the axial lengths of the various layers are not all the same. For example, the rotor 450 may include a first layer portion 452, a second layer portion 454, a third layer portion 456, a fourth layer portion 458, and a fifth layer portion 460. In some configurations, the length of the first layer portion 452 and the fifth layer portion 460 may be half the length of the respective layer portion located between the two layer portions. Each layer section may be assembled such that the groove patterns of adjacent layer sections are different, while the groove patterns of every other layer section are the same. The layer portions at the ends of the rotor axis may have a reduced axial length and may have the same groove pattern.

Another technique for adjusting torque ripple may be by deflecting the rotor. The deflected rotor may be described as a rotor having at least two layer portions, wherein one magnet opening is offset from another magnet opening. The deflected rotor may be combined with various groove patterns to further reduce torque ripple.

Fig. 9A depicts a rotor 500 comprised of two layers, wherein the two layers are not deflected relative to each other. The rotor 500 may be comprised of a first layer portion 506 and a second layer portion 508. The two layers are arranged such that the first layer pole intermediate position 504 and the second layer pole intermediate position 510 are aligned. FIG. 9B depicts the deflected rotor configuration 502. In the deflected rotor structure 502, the first layer portion 506 is rotated relative to the second layer portion 508 such that the first layer portion magnetic pole intermediate position 504 is at an angle relative to the second layer portion magnetic pole intermediate position 510. The deflection of the rotor layer portion may also be applied to rotor constructions comprising more than two layer portions. The rotor layer sections may be aligned such that the pole neutral position for each layer section is rotated compared to the other pole neutral positions. The deflection is described relative to the pole neutral position, but the deflection can be described relative to different reference points on the layer portion. The magnetic pole position defined by each layer portion may be rotated or offset by a predetermined angle from the other layer portion.

In some configurations, the rotor may be comprised of a single layer portion. However, there may be at least two poles with different groove patterns. Fig. 10 depicts a single-layer rotor 550 composed of laminations defining different groove patterns for adjacent poles. For example, the first magnetic pole 552 can have a first associated pattern of grooves 556 and the second magnetic pole 554 can have a second associated pattern of grooves 558. The location at which second groove pattern 558 defines grooves relative to second pole intermediate position 562 can be different than the location at which first groove pattern 556 defines grooves relative to first pole intermediate position 560. In this configuration, first groove pattern 556 and second groove pattern 558 may repeat every other magnetic pole. That is, the groove pattern for the rotor may be repeated on the circumferential surface with an arc length corresponding to two poles of the rotor.

The axial groove pattern may be defined such that adjacent poles have different groove patterns. The pattern of grooves may alternate between the poles about the axis. In some configurations, the groove pattern may be different for three consecutive poles. That is, three consecutive poles do not show the same groove pattern. The groove pattern may be repeated for every group of three poles. In some configurations, the axial groove pattern for the rotor may repeat over the circumferential surface with an arc length corresponding to three poles of the rotor.

Fig. 11 depicts a rotor 600 comprised of a single layer portion. The single layer portion 602 is composed of rotor laminations defining different axial groove patterns for three

consecutive poles

604, 606, 608. The first pole 604 can be associated with a first groove pattern, the second pole 606 can be associated with a second groove pattern, and the third pole 608 can be associated with a third groove pattern. The pattern defined by the three

poles

604, 606, 608 may be repeated such that the groove pattern is repeated around the circumference of the rotor 600. In this configuration, the next pole (not shown) adjacent to the third pole 608 may have the same groove pattern as the first pole 604. The axial groove pattern for the rotor may repeat over the circumferential surface with an arc length corresponding to three poles of the rotor.

The configurations described herein may be combined. The rotor may be composed of multiple layer portions defining different surface groove patterns. Each layer portion may define a different surface groove pattern for each pole. The groove pattern defined by the various layer portions may be repeated over several poles.

Fig. 12 depicts a two-layer rotor construction 650 in which each layer defines a different groove pattern for adjacent poles. First tier portion 660 may include a first slot pattern for first pole 652 and a second slot pattern for second pole 654. The second layer portion 662 may define a third groove pattern for the first pole 652 and a fourth groove pattern for the second pole 654. In some configurations, the same rotor lamination may be used for each layer. However, for each layer, the rotor laminations may be shifted by one pole so that each pole has a different groove pattern across the axial length of the rotor.

Fig. 13 depicts a three layer rotor 700 in which each layer defines a groove pattern for each three poles. A first pole 702, a second pole 704, and a third pole 706 are depicted. A first layer portion 708, a second layer portion 710, and a third layer portion 712 are also depicted. The first layer portion 708 may be composed of rotor laminations defining a first groove pattern for the first pole 702 while the surfaces for the second pole 704 and the third pole 706 are smooth. The second layer portion 710 may be composed of rotor laminations defining a second groove pattern for the second pole 704 while being smooth for the surfaces of the first pole 702 and the third pole 706. The third layer portion 712 may be composed of rotor laminations defining a third groove pattern for the third pole 706 while the surfaces for the second pole 704 and the first pole 702 are smooth. The groove pattern for each layer portion may be repeated every three poles.

Fig. 14 depicts a single layer rotor lamination 800 for a rotor that may include a single layer portion where the groove pattern is different for each pole. An eight pole rotor is described wherein each pole has a different axial groove pattern. The number of axial grooves defined for

rotor poles

802 and 816 may be different for each pole. For example, the first rotor pole 802 may define four axial grooves on the circumferential surface. The third rotor pole 806 and the seventh rotor pole 814 may define three axial grooves on the circumferential surface. The fifth rotor pole 810 and the sixth rotor pole 812 may define two axial grooves on the circumferential surface. The second rotor pole 804 and the eighth rotor pole 816 may define an axial groove on the circumferential surface. The fourth rotor pole 808 may define a smooth circumferential surface without any axial grooves. The axial groove pattern may vary based on the number of axial grooves defined and the arrangement of the axial grooves relative to the mid-position of the poles.

FIG. 15 depicts a single-layer rotor lamination 900 in which each pole defines two axial grooves ₁918 separate axial grooves the second rotor pole 908 may be defined at an angle α ₂920 axial grooves separated third rotor pole 910 may define an angle α ₃922 spaced apart axial grooves fourth rotor pole 912 may define an angle α ₄924 spaced apart axial grooves the fifth rotor pole 914 may define an angle α ₅926 spaced apart axial grooves the sixth rotor pole 916 may define an angle α ₆928, an axial groove, the seventh rotor pole 902 may define an angle α ₇930 separate axial grooves the eighth rotor pole 904 may define an angle α ₈932 separate axial grooves. In some configurations, angles 918-932 may be different for each pole. In some configurations, angles 918-932 may be alternating values.

In some configurations, the rotor may include multiple layer portions with alternative groove patterns on a predetermined number of poles. For example, the first layer portion may define a first groove pattern that repeats every two poles. The second layer portion may define a second groove pattern that repeats every two poles. The groove pattern for the first layer portion and the second layer portion may be different for each magnetic pole.

The orientation of the axial grooves and the number of layer portions within each pole may be determined to reduce selected harmonics. Here, the figures herein depict axial grooves, but it is contemplated that the number of grooves and the positioning of the axial grooves may vary based on the particular motor design. The number of layer sections used may also vary based on the particular motor design.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. As previously described, features of multiple embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments may have been described as providing advantages or being advantageous over other embodiments or prior art implementations in terms of one or more desired characteristics, those of ordinary skill in the art will recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, depending on the particular application and implementation. These attributes may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, maintainability, weight, manufacturability, ease of assembly, and the like. Accordingly, embodiments described as inferior in one or more characteristics to other embodiments or prior art implementations are not outside the scope of the present disclosure and may be desirable for particular applications.

Claims

1. A permanent magnet electric machine comprising:

a rotor including a plurality of magnetic poles arranged around an axis, each magnetic pole corresponding to a predetermined arc length of a circumferential surface of the rotor formed of a plurality of laminations stacked axially defining a plurality of axial grooves for each magnetic pole on the circumferential surface of the rotor such that a pitch between the grooves is different for each magnetic pole relative to the other magnetic poles.

2. The permanent magnet electric machine according to claim 1, wherein the plurality of axial grooves is two axial grooves for each pole.

3. The permanent magnet electric machine according to claim 2, wherein the plurality of axial grooves are defined by an angle between the axial grooves of each pole for each pole, and the angle is different for each pole.